1. Technical Field of the Invention
The present invention relates generally to the field of micro-electromechanical switches, and, more particularly, to an apparatus and method of forming resistors and switch-capacitor bottom electrodes.
2. Description of Related Art
Rapid advances made in the field of telecommunications have been paced by improvements in the electronic devices and systems which make the transfer of information possible. Switches which allow the routing of electronic signals are important components in any communication system. Electrical switches are widely used in microwave circuits for many communication applications such as impedance matching, adjustable gain amplifiers, and signal routing and transmission. Current technology generally relies on solid state switches, including MESFETs and PIN diodes. Switches which perform well at high frequencies are particularly valuable. The PIN diode is a popular RF switch, however, this device typically suffers from high power consumption (the diode must be forward biased to provide carriers for the low impedance state), high cost, nonlinearity, low breakdown voltages, and large insertion loss at high frequencies.
The technology of micro-machining enables the fabrication of intricate three-dimensional structures with the accuracy and repeatability inherent to integrated circuit fabrication offering an alternative to semiconductor electronic components. Micro-mechanical switches offer advantages over conventional transistors because they function more like mechanical switches, but without the bulk and high costs. These new structures allow the design and functionality of integrated circuits to expand in a new dimension, creating an emerging technology with applications in a broad spectrum of technical fields.
Recently, micro-electromechanical (MEM) switches have been developed which provide a method of switching RF signals with low insertion loss, good isolation, high power handling, and low switching and static power requirements. Systems use single MEM switches or arrays of switches for functions such as beam steering in a phased array radar for example. The switches switch a high frequency signal by deflecting a movable element (conductor or dielectric) into or out of a signal path to open or close either capacitive or ohmic connections. An excellent example of such a device is the drumhead capacitive switch structure which is fully described in U.S. Pat. No. 5,619,061. In brief, an input RF signal comes into the structure through one of two electrodes (bottom electrode or membrane electrode) and is transmitted to the other electrode when the membrane is in contact with a dielectric covering the bottom electrode.
MEM devices can also be integrated with other control circuitry to operate well in the microwave regime. For example, to operate as a single-pole double-throw switch (SPDT) for directing signals of power flow between other components in a microwave system, the MEM switch is placed in circuit with passive components (resistors, capacitors, and inductors) and at least one other switch. However a problem exist when this type circuit integration is attempted to be realized in silicon because of the diverse temperature processes of MEM components (such as the electrodes) and passive components (such as bias resistors). Therefore, there exist a need for a method of efficiently fabricating a micro-electromechanical switch by simultaneous formation of component resistors and switch electrodes.